The present invention relates generally to a plate heat exchanger.
Openable and permanently joined conventional plate heat exchangers are normally constructed with equally sized inlets and outlets for respective heat transfer media. For one-phase heat transfer, equally sized inlets and outlets are satisfactory with respect to flow velocity and pressure drop, since the specific volume for the media does not change considerably over the temperature range to which the media is exposed during the heat transfer.
In two-phase heat transfer, such as during concentration or evaporation, the media is supplied in liquid-phase and discharged in gas-phase, which has a considerably larger specific volume than the liquid-phase, wherein the flow velocity and the pressure drop in the outlet become larger than in the inlet. With equally sized inlets and outlets, imbalance may appear between different ducts in the plate heat exchanger.
According to one known plate heat exchanger, a restriction means is provided in respective inlets between two adjacent heat transfer plates to obtain an equal distribution of the incoming fluid. The restriction means may consist of a ring or a washer, which is provided with a hole and which is arranged between each pair of adjacent heat transfer plates. The restriction means can also consist of a pipe which has several holes and is arranged in the inlet port channel of the plate heat exchanger. As an alternative, the restriction means can be formed of the heat transfer plates themselves, whereby the edge of the ports of two adjacent heat transfer plates are folded edge to edge to each other except for a short distance, which forms an opening.
The aforementioned restriction means generally have not performed satisfactorily. Problems have arisen in the production of the plate heat exchanger. The use of separate rings or washers has proved far too expensive and it has been difficult to position the rings or the washers properly during assembly. A restriction means in the shape of a pipe must be adapted to the number of heat transfer plates included in the plate heat exchanger and also must be located correctly with respect to the inlet passages between the heat transfer plates. Thus, such pipes generally are not used in the serial production of plate heat exchangers. The proposed folding of the edge of the port has not proved practicable, because the heat transfer plates are made of thin plates and it is difficult to obtain a well-defined opening in the plate interspaces.